The present invention relates to the conversion of carbonaceous feedstock into useful products. The term “carbonaceous feedstock” as used herein includes not only organic matter that is part of the stable carbon cycle, but also fossilized organic matter such as coal, petroleum, and natural gas, and products, derivatives and byproducts thereof such as plastics, petroleum coke and the like. The first step in such processes is the gasification of the feedstock in a so-called “reformer” to a stream of hydrogen, carbon monoxide, carbon dioxide and methane. This stream is referred to as syngas, and its generation is disclosed in U.S. Pat. No. 4,872,886, and others. The '886 patent includes an oxidation first step, in which air is used to fire a portion of the feedstock. The resulting stream is then combined with a “coal slurry” stream in a second stage of the conversion reaction. U.S. Reissue 35,377 discloses the anaerobic reaction of the feedstock with steam.
The various ingredients in a stream of syngas can then be converted into other compounds in a so-called Fischer-Tropsch reactor. The catalyst used in the reactor, and to some extent the temperatures and pressures used, will determine what products can be obtained.
The Fischer-Tropsch reaction disclosed at the bottom of page 106 in Organic Chemistry, Third Edition, by Brewster and McEwen, ©1961 shows the conversion of carbon monoxide and hydrogen to alkanes over a cobalt-thoria catalyst. U.S. Pat. No. 4,752,622 discloses and claims the use of a three component catalyst comprising molybdenum or tungsten, cobalt or nickel, and an alkali or alkaline earth promoter, to produce methanol from carbon monoxide and hydrogen. U.S. Pat. No. 4,609,679 selectively catalyzes for the production of methane, by using ruthenium combined with tantalum, niobium, vanadium or mixtures thereof. U.S. Pat. No. 4,675,344 (Canadian CA 1,267,160) controls the ratio of methanol to higher alcohols produced by using molybdenum or tungsten sulfide catalysts, and adjusting the concentration of a sulfur releasing substance in the feed.
The conversion of methanol to ethanol and higher alcohols in the presence of carbon monoxide and hydrogen is disclosed in U.S. Pat. No. 4,825,013 and its Canadian counterpart CA 1,268,189. The patent claims achieving this conversion through the use of a heterogeneous catalyst comprised of molybdenum or tungsten and an alkali or alkaline earth element.
German Patent Application 32 42 697 A1 is directed towards a process for the concurrent production of methanol and ethanol by catalytically converting synthesis gas into methanol and separating the methanol from the reaction mixture. The separated methanol, along with excess gas remaining, is converted to ethanol at an increased pressure and an increased temperature, using a cobalt catalyst. In this process methanol, as well as ethanol, is produced from a single raw substance in a two-step process, using a heterogeneously catalyzed system with a homogeneously catalyzed system. Fresh synthesis gas is added if the excess gas does not contain enough carbon monoxide prior to homologization.
In European patent application 849,245, natural gas is converted in a reformer to a syngas stream of carbon monoxide, carbon dioxide, hydrogen and unconverted methane. This entire syngas stream is passed through a Fischer-Tropsch reactor to produce methanol. The unreacted syngas is divided into a CO, CO2 and CH4 stream, which is recycled back through the reformer; and a hydrogen rich stream, which is combined with oxygen and combusted to provide heat for the reformer.
PCT patent application WO 82/02547 removes CO2 from a syngas stream and recycles it through a reformer along with steam and an incoming stream of methane. The reactants produce a syngas stream from which the CO2 is thus continuously removed and recycled.
European patent application 253,540 is exemplary of art in which higher alcohols are produced in a Fischer-Tropsch reactor from feedstock (coal slurry) syngas, and any methanol produced is recycled through the Fischer-Tropsch reactor.